1. Field of the Invention
This invention relates to a process for forming a dinitramide salt, or dinitramidic acid, by reaction of a salt or free acid of an N(alkoxycarbonyl)N-nitroamide and a nitronium-containing compound such as N.sub.2 O.sub.5, a nitryl halide, or a nitronium salt to form an intermediate product, which is then reacted with a base to form the dinitramide salt, or with an alcohol to form dinitramidic acid.
2. Description of the Related Art
Solid oxidizers, such as ammonium perchlorate or potassium perchlorate, have been used in the past in rocket propellant formulation because of their improved ease of storage over liquid oxidizers. However, the presence of a halogen in the solid oxidant produces a visually observable smoke trail which is also observable on radar as well. Also, chlorine poses a serious atmospheric environmental hazard of ozone depletion and acid rain.
Because of such shortcomings in the use of perchlorate solid fuel oxidizers, other materials, including nitrate (NO.sub.3.sup.-) compounds, have been investigated in the search for oxidizers which would provide the desired energy density and stability, without the drawbacks of the perchlorate oxidants.
In related application Ser. No. 07/540,020, filed by several of us on Jun. 18, 1990, now issued as U.S. Pat. No. 5,254,324 on Oct. 19, 1993, and assigned to the assignee of this invention and cross-reference to which is hereby made, we disclosed and claimed new ionically bound compounds suitable for use as oxidizers in rocket propellants. These compounds comprise dinitramide salts of metals or nitrogen-containing cations. We also described and claimed in that application a method of making such nitramide salts by first forming a dinitramine compound and then reacting the dinitramine compound with either a nitrogen-containing compound or a metal salt.
In related application Ser. No. 07/539,647, also filed by several of us on Jun. 18, 1990 and assigned to the assignee of this invention and cross-reference to which is hereby made, we disclosed and claimed another method of forming the dinitramide salts of metals or nitrogen-containing cations claimed in application Ser. No. 07/540,020. This second method of making such nitramide salts comprises nitrating a carbamate to form a dinitramide acid intermediate product, followed by neutralizing the intermediate product with a compound selected from the class consisting of ammonia, hydrazine, a primary amine, a secondary amine, and a salt having the formula AX where A is a metal ion or a nitrogen-containing ion and X is a fluoride, chloride, hydroxyl, carbonate, alkoxide, or carboxyl anion.
In related application Ser. No. 07/737 757, filed by us with another on Jul. 30, 1991, now issued as U.S. Pat. No. 5,316,749 on May 31, 1994, and assigned to the assignee of this invention and cross-reference to which is hereby made, we disclosed and claimed yet another method of forming ammonium dinitramide salt by the reaction of ammonia and a nitronium-containing compound such as nitronium tetrafluoroborate or nitronium nitrate.
It is also known to react a nitronium salt with an organic nitramine to form a covalently bonded N,N-dinitramine compound. Hamel et al. U.S Pat. No. 3,428,667 describes the reaction of an ionic nitronium salt with a primary organic nitramine to form N,N-dinitramines having the general formula R--[N(NO.sub.2).sub.2 ].sub.n where n is 1-2 and R is a monovalent or divalent organic radical. These compounds are said to be highly energetic and useful as ingredients in propellant, explosive, and pyrotechnic compositions.
However, as discussed in our related applications, the formation and use of covalently bonded nitrogen-containing solid fuel oxidizing agents for use in rocket propellant formulations is not as desirable as the use of the previously claimed dinitramide salts because these salts have been found to be much more stable. The processes for forming such stable dinitramide salts in the aforementioned U.S. Pat. Nos. 5,254,324 and 5,198,204 have been multiple step processes involving the formation of precursors which must then be isolated or recovered for a further reaction with another reactant to form the desired ionically bonded dinitramide salt product. It would be desirable to provide a simplified process to form an ionically bonded stable dinitramide salt wherein one reaction vessel may be used to form the dinitramide salt product.
It would also be desirable to provide a method for the formation of such dinitramide salts which would provide a high yield, i.e., .about.50%, while only using one mole of nitronium reactant per mole of other reactant, as opposed to the method described in U.S. Pat. No. 5,316,749, wherein the desired ammonium dinitramide salt is formed by reacting one mole of ammonia with two moles of nitronium-containing compound.